1. Field of the Invention
The present invention relates to a starting device for discharge lamp, particularly suitable to a lamp lighting device for vehicle headlights.
2. Brief Description of the Prior Art
The Lamp lighting device for vehicle headlights having a starting transformer equipped with a core is now widely used. But in this starting transformer the core should be form voluminous in order to avoid an electric current saturation phenomenon that sometimes occurs in the starting transformer equipped with the above-mentioned core. In other words, inductance value in the ordinary transformer, usually equipped with the core, reaches a saturated value (corresponding to the inductance value of a coreless transformer), at a certain electric current value, as shown in FIG. 5 where inductance characteristic curves against electric current value are depicted.
Magnetic properties of the core are influenced by ambient temperature. FIG. 6 is a figure for determining Curie temperatures in the respective core types depicting relations between temperature T (xc2x0 C.) and initial permeability (xcexci) values of A type (a broken line) and B type (a solid line) cores used at a relatively lower temperature (below 100xc2x0 C.) and at a relatively higher temperature (below 150xc2x0 C.) respectively.
The Curie temperature of A type is 174xc2x0 C. for the lower temperature use and that of B type is 200xc2x0 C. for the higher temperature use. Since a ferrite core has a critical temperature (Curie temperature) where the core transforms from ferromagnetic to paramagnetic, the ferrite core with the higher Curie temperature should be used at a higher temperature range (100xc2x0 C.xcx9c200xc2x0 C.).
When an HID lamp is employed as the discharge lamp, the core with Curie temperature above 200xc2x0 C. should be selected for the starting transformer from a safety point, since heat from the lamp raises the temperature of the core up to ca. 150xc2x0 C. due to a short distance between the lamp and the core when a starting circuit is arranged in a lamp socket. The higher Curie temperature of the core is, the lower the initial permeability (xcexci) of the core is (i.e. a lower inductance value when coil turns are kept constant), which means lower performance. Since such core is not usually employed, quantity of the commercially manufactured core is small, which naturally leads to a cost increase.
When ferrite type cores are molded by an epoxy resin etc. for insulation, fatal defects such as ruptures or cracks are sometimes formed due to a shrinkage difference between the core and the molded resin. In order to avoid the above-mentioned defects caused by the shrinkage of the molded resin, the core has to be closed in a bobbin etc. or the core with a simple shape (round or rectangular rod etc.) is required.
In the conventional starting device for discharge lamp with the above-mentioned core, a supporting point of the core was easily broken by vibrations and impacts etc. because of a core weight. As measures against such breakage a core supporting mechanism was reinforced or other supporting members were added. Which resulted in a manufacturing cost increase.
The present invention is carried out in view of the above-mentioned problems so as to provide a small sized and light weighed starting device for discharge lamp free from breakage due to vibrations and impacts, as well as the inexpensively arranged starting device.
The starting device for discharge lamp is constituted as follows:
(1) The starting device for discharge lamp equipped with a socket for mounting the discharge lamp and a starting device member; where the starting device has a starting transformer comprising a bobbin for mounting the starting transformer and a core-less coil structure consisting of a primary and a secondary coils wound around the bobbin.
(2) The starting device for discharge lamp according to (1) where the diameter of the core-less portion of the starting transformer is set between 0.1 mm to 10 mm and one end of the secondary coil is led through the core-less portion and electrically connected to a high voltage electrode.
(3) The starting device for discharge lamp according to (1) where the core-less portion of the starting transformer is formed in a column with a circular or rectangular cross section, coil winding portions of the bobbin are formed in circular shape for divided winding and aligned the same axis as the center of the socket.
(4) The starting device for discharge lamp according to one of the (1) to (3) where leading wires from respective coils of the starting transformer is fitted in notches formed on a hollow wall of a rear side of a socket case and fixed to the wall by clips.
(5) The starting device for discharge lamp according to (1) where the starting device has a harness equipped with a connector.
(6) The starting device for discharge lamp according to (1) where the starting device has a direct coupler.